Why couldn't colonists use indentured servants as they had in the past

I believe colonists stopped using indentured servants as they had in the past because it wasn't profitable anymore. Indentured servants came to America of their own free will, and they were being paid for their work, however small that amount may have been. On the other hand, this was the time when slavery in America began, and slaves worked for free, so having slaves instead of indentured servants was much more lucrative.